Cyclic olefin polymers and cyclic olefin copolymers (also referred to as “COP” or the like and “COC” or the like, respectively), which have low hygroscopicity and high transparency, are used for various applications including those in the field of optical materials, such as optical disk substrates, optical films, and optical fibers. Representative examples of COC include a copolymer of cyclic olefin and ethylene. The glass transition temperature of such a copolymer can be altered by varying a copolymer composition of cyclic olefin and ethylene. This enables manufacture of a copolymer having a glass transition temperature (Tg) higher than that of COP. Even a Tg of more than 200° C., which is difficult to be obtained for COP, can be achieved. However, disadvantageously, COC is hard and brittle, and has low mechanical strength, poor handling properties, and insufficient processability.
Various high-Tg polymers are currently available. However, they have polar groups, and thus show limited hygroscopic and dielectric properties. Accordingly, there have been demands for a high-Tg polymer having an olefin based backbone but not having a polar group and showing excellent optical properties, dielectric characteristics, and mechanical strength.
One of the approaches for improving the mechanical strength of a high-Tg COC involves copolymerizing a cyclic olefin with an α-olefin other than ethylene (hereinafter, referred to as a “specific α-olefin”). Various studies have been conducted about copolymerization of a cyclic olefin and a specific α-olefin.
Copolymerization of a cyclic olefin and a specific α-olefin significantly differs from that of a cyclic olefin and ethylene. When a cyclic olefin is copolymerized with a specific α-olefin, a chain transfer reaction due to the specific α-olefin may occur under the conditions where a high molecular weight product can be obtained by copolymerizing a cyclic olefin with ethylene. Because of this, a high molecular weight product has been difficult to be obtained. Therefore, a copolymer of a cyclic olefin and a specific α-olefin has been considered to be unsuitable for a forming material (see, for example, Nonpatent Document 1).
Patent Document 1 describes that a high molecular weight product formed from a cyclic olefin and a specific α-olefin was obtained in the presence of a specific Ti-based catalyst, and that a film with excellent physical properties was obtained having a Tg of 245 to 262° C., a low hygroscopicity, and a linear expansion coefficient of less than 80 ppm. However, large amounts of a catalyst and a co-catalyst are used for the polymerization method disclosed in Patent Document 1. This may leave the following problems: the saving of resources is difficult; the production cost of a copolymer is high; and the transparency of a film is impaired by a residual catalyst and co-catalyst. Note that 92 to 164 g of a copolymer can be obtained per gram of a catalyst in Patent Document 1.
Patent Document 2 discloses a film having an excellent punching property, but its Tg is less than 170° C. Further, large amounts of a catalyst and a co-catalyst are used in Patent Document 2, resulting in the following problems: the saving of resources is difficult; the production cost of a copolymer is high; and the transparency and thermal stability of a film is impaired. Note that 127 to 275 g of a copolymer can be obtained per gram of a catalyst in Patent Document 2.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2009-298999    Patent Document 2: Japanese Patent No. 5017222    Non-Patent Document 1: Jung, H. Y. et al., Polyhedron, 2005, 24, pp. 1269-1273